1. Field of the Invention
This invention relates to a bulb socket, and particularly to a bulb socket which can prevent the electrical contacts therein to be pulled out or to become shortcircuited by using a fastening structure.
2. Description of the Prior Art
In a conventional and festival decoration bulb socket, the lower buttom of the socket has a channel for mounting power-supply wires; the bottom surface of the socket is mounted with two grooves for inserting two electrical contacts. The prongs of the electrical contacts extend into the grooves; after the power-supply wires are mounted in a channel, a fastening cover is fastened in the channel, and then the prongs of the electrical contacts will pierce through the insulator of the power-supply wires respectively to fulfill electric connection. The end portions of the electrical contacts extend upwards into the socket for connecting the bulb electrodes. The flange of the electrical contact will be in contact with the bulb base; such products are manufactured in Taiwan and in China mainland.
The aforesaid bulb socket caused a short-circuit accident in the United States in 1993 upon being used by children; the short-circuit accident was resulted in the flange portion and the bent plate portion. Such accident did happen, though it has passed the UL test; as a result, the UL has re-established their new standards to test the safety of such products. In accordance with the new standards of UL, the side and center contacts shall be supported, restrained, or constructed such that when subjected to a 3 lbf (13.3 N) applied in any direction, they can not become contacted each other, and a lamp screw base causes a short circuit when a lamp is installed. The screw threads inside the socket should keep a bulb therein without being pulled out upon applied with a given force; the screw threads should not become wear-and-tear. When the socket is pressed, the copper plate should not deform and dislodge.
However, both the conventional sockets and the socket disclosed in some patents (such as Taiwan patent Nos. 82209610, 82207093, 82215955 and 82218418) not do conform to the US standards; particularly, the screw threads in the bulb socket fail to meet that standards; for instance, in Patent '418, the screw threads are made with a direct ejection method, i.e., it is impossible to pass the new test standards. Other patents, such as '610, '093, and '955, the sockets thereof are made of copper with good screw threads, but the fastening method of the socket and the base is poor, i.e., by using a reverse hook, which is unable to withstand a pulling test.